The present invention relates to radon gas concentration level measurement. More specifically, the present invention relates to radon gas sample collection methods for producing representative gas samples for subsequent analysis.
Radon gas, which is a radioactive decay by-product of radium, constantly seeps from subterranean radium deposits and out through the surface of the earth's crust, into the atmosphere surrounding the earth.
Significant concentrations of radon gas have been shown to pose possible health threats to people. Radon gas, in concentrations above four pico-curies per liter, (4 pCi/1) has been statistically shown to increase the risk of cancer in individuals exposed to such concentration levels. Since radon gas has a relatively short half-life, in the order of four days, the radon gas concentration never reaches significant levels upon escaping into the earth's atmosphere. Without confinement, radon gas does not reach sufficient concentration levels to pose a human health hazard.
Recently, however, radon gas has begun to pose a human health problem. If an enclosed structure, such as a dwelling, or office building, is placed over an area of radon effluence, the radon can seep into the structure through cracks or other openings in parts of the foundation or other parts of the structure that are in contact or near contact with the earth below the structure. If the structure is well-ventilated, radon concentrations still will not develop to sufficiently high levels to pose a human health hazard. However, with the advent of modern insulation techniques, and with the current considerations given to fuel and energy efficiency, most modern buildings are sufficiently weathertight so as not to permit a free exchange of interior and exterior air. This lack of air exchange can cause significantly increased radon concentrations to develop within a building.
At present, no reliable geological techniques are available for prediction of high concentrations of radon gas, or high concentrations of underground radium deposits. It is equally impossible to predict the extent of radon seepage into a building prior to construction. Therefore, it is necessary to measure actual radon level concentrations within a structure after construction has been completed to the extent that the structure is sealed against free air exchange.
At present, many techniques are available for measurement of radon concentration levels within closed atmosphere conditions. The Environmental Protection Agency (EPA) has developed measurement protocols for seven measurement systems. The advantages and disadvantages of those systems is reviewed in the EPA publication, "Radon/Radon Progeny Cumulative Proficiency Report" (EPA-No. 5201/1-86-008), incorporated herein by reference. The seven tested measurement systems include, alpha track detectors, charcoal canister gas collectors, continuous radon gas monitors, continuous working level monitors, grab radon gas sampling, grab working level sampling and radon progeny integrated sampling. The most common testing method offered by laboratories participating in the EPA testing is the "charcoal canister" method, wherein a mechanically-dried quantity of activated charcoal a material having a high surface-area-to- weight ratio, is passively exposed to the radon-containing atmosphere for a set extended period of time. The charcoal then becomes partially saturated with radon gas. The charcoal canister is then placed in a photospectrometer and the natural radioactive decay products of the radon gas trapped in the charcoal, are measured. Based upon the rate of production of decay products of radon gas, a determination is made as to the concentration of radon gas to which the charcoal has been exposed.
Other methods, such as a continuous radon monitor or a continuous working level monitor, can give a continuous real time indication of present radon levels within the atmosphere to which these devices are exposed. These devices are considerably more expensive, cumbersome and complicated to use than an activated charcoal collector.